Southeast Basin Interceptor and Siphon

Richmond’s Southeast Sanitary Basin was experiencing surcharging and sanitary sewer overflows (SSOs) during wet weather events. To address these issues, Donohue & Associates completed a comprehensive plan that considered existing and future land usage, existing sewer conditions, and future anticipated sewer requirements. A SWMM model was built using flow monitoring and GIS data supplied by the District.

Donohue prepared plans and specifications for the recommended improvements. This included 23,000 feet of 12- to 30-inch interceptor sewer parallel to the existing sewer system at depths up to 25 feet and nearly 2,000 feet of 18-inch siphon parallel to existing triple barrel siphon lines. The design included 13 interconnection points between the new and existing sewer lines to relieve flow from the existing interceptor when surcharging occurs.

A unique feature of the new sewer system is a siphon cleanout system that allows individual siphons to be taken out of service and cleaned. A drainout manhole was placed at the low point of the lines and connected to the existing and new siphon lines by a series of valves, cleanout structures and wye sections.

The project design was completed in 6 months in order to allow construction to be completed prior to a state-mandated deadline.